add pre-commit config for flake8

docs/Makefile

@@ -17,4 +17,4 @@ help:
 # Catch-all target: route all unknown targets to Sphinx using the new
 # "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
 %: Makefile
-	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)

docs/flaskstyle.sty

@@ -9,7 +9,7 @@
   \begin{titlepage}%
     \let\footnotesize\small
     \let\footnoterule\relax
-    % Apply following fix only on PDF output, i.e. pdfoutput macro is not 
+    % Apply following fix only on PDF output, i.e. pdfoutput macro is not
     % undefined
     \ifx\pdfoutput\undefined\else
       \begingroup

docs/patterns/appfactories.rst

@@ -93,13 +93,13 @@ To run such an application, you can use the :command:`flask` command::
 
     $ export FLASK_APP=myapp
     $ flask run
-    
-Flask will automatically detect the factory (``create_app`` or ``make_app``) 
+
+Flask will automatically detect the factory (``create_app`` or ``make_app``)
 in ``myapp``. You can also pass arguments to the factory like this::
 
     $ export FLASK_APP="myapp:create_app('dev')"
     $ flask run
-    
+
 Then the ``create_app`` factory in ``myapp`` is called with the string
 ``'dev'`` as the argument. See :doc:`/cli` for more detail.